Osmosis is best defined as the movement of water molecules
- A. from a region of low water potential to one of high water potential
- B. against a concentration gradient using ATP
- C. from a region of higher water potential to one of lower water potential through a partially permeable membrane
- D. along with dissolved solutes through a partially permeable membrane
Explanation
Water always moves down its own water potential gradient, that is from the more dilute solution to the more concentrated one, and the membrane is what stops the solute simply moving the other way. Osmosis is a special case of diffusion, so it is passive and needs no ATP. Defining it in terms of water potential rather than concentration avoids the confusion of talking about the concentration of water itself.
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